The continued development and implementation of wireless communications systems has made it possible to transmit a large amount of data over a radio frequency (RF) air interface. There are a number of technologies that can be used to broadcast video and other programming from a central location to a receiver device. Forward Link Only (FLO) is an example of a transmission methodology that uses a radio frequency (RF) air interface to broadcast video and other programming from one or more central locations to one or more receiver devices. The basic structure of a packet in FLO is referred to as a “superframe.” A superframe contains 1200 orthogonal frequency division multiplexed (OFDM) data symbols and has a duration of one (1) second. A superframe contains pilot, control and data frames. Typically, four data frames, each containing one or both of wide-area and local-area data are part of a superframe. Because the receiver device is typically powered by a small, rechargeable power source, such as a battery, power conservation and the overall minimization of power consumption are highly desirable.
One of the ways to minimize power consumption in a FLO system is referred to as “early exit.” The amount of processing performed on the received signal by the portable receiver is variable, based on a number of different attributes of the received signal, and other parameters. The term “early exit” refers to minimizing the amount of processing performed on a received signal by “exiting” the receiver processing function prior to decoding all of the received data. For example, in the current FLO system, turbo packets are decoded upon arrival. After turbo decoding (TD), a cyclic redundancy check (CRC) is performed to determine whether the turbo packet has been successfully decoded. When a Reed-Solomon (RS) code having a (16, 12) format is adopted as an outer code in FLO, systematic turbo packets will be scheduled in frames 1 to 3 and frame 4 contains all RS coded parity packets. As a result, at the end of frame 3, if all systematic turbo packets are decoded, there is no need to get RS coded parity packets in frame 4 and the receiver processing can be terminated early (referred to as early exit) to save power and to reduce channel switching time.
The FLO methodology has been improved to increase bandwidth and data carrying capability. The enhanced FLO system is referred to as FLO-EV. In FLO-EV, a long turbo codeword (LTC) is interleaved across frames in one superframe. If one frame is missing, the LTC can be viewed as a randomly punctured turbo code of a higher rate. Therefore, as long as the punctured turbo code rate is less than 1, the superframe is still decodable without frame 4 under high signal-to-noise ratio (SNR) conditions. For some modes, a punctured LTC could be decodable even without frame 3 and 4. An early exit methodology for FLO-EV has greater flexibility than for FLO since it is not limited by the outer RS code rate. For example, in FLO, early exit is not possible when a RS code of (16, 14) is used. Moreover, a punctured LTC in FLO-EV still captures time diversity of 3 frames without frame 4 while turbo packets in FLO do not capture any time diversity. Therefore, if receiver could know whether the punctured LTC is decodable before decoding, FLO-EV could provide significant power saving using an early exit methodology.
However, the physical layer coding structure of FLO-EV is completely different from that of FLO. The relatively simple early exit methodology for FLO cannot be used in FLO-EV because each turbo codeword can no longer be decoded on the fly as in FLO. Therefore, the CRC information is not reliable without TD.
Therefore, it would be desirable to have a way to reduce receiver processing in a FLO-EV system.